Conventional unstackers, e.g. as described in U.S. Pat. No. 1,428,149, comprise an entrainment roller and a counterpressure roller whose parallel shafts are movable toward and away from each other; the entrainment roller has a peripheral recess terminating at its trailing end in a hook which engages an edge of a sheet deposited in that recess with the aid of pick-up means such as levers or bars carrying suction cups. As the sheet moves into the nip of the counterrotating rollers, it is bent around the hook and is then positively entrained to a release point for delivery to a conveyor or other receiving equipment.
Devices of this character are not suitable for use with sensitive sheet material which may be damaged by the bending. Moreover, the recess with its hook must be adapted to the sheet thickness so that different entrainment rollers are required for different thicknesses.